SSC JE Civil Engineering 23-Sep-2019 Shift 2 Solved Paper

Since the effect of curvature is to increase the staff readings and that of refraction is to decrease them and also the effect of curvature is greater than that of refraction, the combined effect is therefore, to increase the staff readings, hence the combined correction is subtractive.
The combined error due to earth's curvature and refraction :
And true staff reading = observed staff reading – 0.0673 D‌2
Where, C‌c = 0.0673 D‌2
The combined correction can be application two ways:
(i) By decreasing each staff reading by the amount 0.0673 D‌2 and then finding, the reduced levels.
(ii) By first finding the reduced levels of the points in the usual way and then increasing them by the amount 0.0673 D‌2 .